抄録
In recent years, whiteness of common salt has increased with improvement of its quality. Though having shown frequently negative values in high quality salt, whiteness values expressed by ΔR andα+βhad good correlation with whiteness by perception in negative region of ΔR as in positive. Thus, whiteness in terms of ΔR seemed to be convenient for the color specification of common salt because of ease in measurement, which, however, was not expressed by absolute value. Visual white point having been below-2.9, perhaps to be about-6 as ΔR, whiteness should be expressed in terms of color difference from ΔR=-6. The zero point of ΔR was located on a straight line combining white point of chromaticity coordinate with the point of x=y=0.3132, and ΔR was defined as distance from this straight line. Negative value of ΔR in case of high quality salt was attributable to blue color, which was caused by transmission and absorbance of incident light. Judd's whiteness and one by perception had no linear relation for high quality salt, namely the former decreased in the negative region of ΔR.
